NEW DELHI (Reuters) -- India has put its nuclear power plants on alert and tightened security after intelligence about possible attacks, a report said.

The step comes after a man arrested in the United States on charges of plotting attacks in India was found to have traveled to Indian states that have nuclear installations, the Press Trust of India (PTI), the country's biggest news agency, said.

PTI quoted unnamed sources in the home ministry as saying that state governments had been asked to step up security around their nuclear plants as a "precautionary measure."

"The step is precautionary in nature. The states have been asked to increase the vigil and patrolling to thwart any sabotage attempt aimed at these vital facilities," a Home Ministry official was quoted as saying by the news agency.

Indian media often reports security alerts based on unnamed intelligence sources.

A senior Home Ministry official, who is not authorized to speak to the media, told Reuters that some states had been asked to tighten security around "vital installations," without giving out more details.

Today's report came only days before the first anniversary of the militant attacks in Mumbai that killed 166 people, and there have been various reports of attacks being planned in India, including from Israel and Australia, around this time.

U.S. authorities arrested David Headley, a U.S. citizen, on October 3 on charges of hatching a plot to attack a Danish newspaper whose cartoons of the Prophet Muhammad led to deadly protests by Muslims.

New Delhi has asked to interview Headley over possible plans to attack Indian targets and are investigating various visits to the country.

The U.S. government said Headley also traveled to Pakistan where he met a leader of a group with ties to Al-Qaeda, Harakat-ul Jihad Islami, and communicated with members of the militant group Lashkar-e-Taiba, according to the U.S. government.

India blames the Lashkar-e-Taiba for carrying out several attacks in Indian cities, including last November's strikes on Mumbai.